Field of the Invention
The present invention relates to a photothermal conversion spectroscopic analyzer, and particularly relates to the photothermal conversion spectroscopic analyzer using a thermal lens effect.
Description of the Related Art
When a sample is irradiated with a focused light, the sample absorbs the light and temperature rises locally. With this temperature rise, a refraction index of the sample is changed. In many substances, there is an optical effect such as a concave lens generated near a light focusing portion of the sample because the refraction index is decreased due to temperature rise. This effect is generally called a thermal lens effect, and sample measurement utilizing this effect is used as a high-sensitivity measuring method for a non-fluorescent substance.
FIG. 6A is a schematic configuration diagram illustrating an exemplary related art in which a photothermal conversion spectroscopic analyzer 302 uses a transmission optical system using the above-described thermal lens effect (JP-2005-164614-A). In FIG. 6A, an excitation light L1 emitted from an excitation light source 101 and a probe light L2 emitted from a probe light source 102 are multiplexed on a same optical axis at a first filter 103, and the multiplexed light enters a sample 109 contained in a sample cell 107 after having passed through a first condenser lens 106, such as an objective lens. The excitation light L1 has a characteristic to be partly absorbed in the sample 109. Therefore, the excitation light L1 focused in the sample 109 by the first condenser lens 106 locally heats the sample 109 in a light focusing area. Then, the excitation light L1 is absorbed at a third filter 110. On the other hand, a probe light L2 passing through the optical axis same as the excitation light L1 has a spreading angle of a light beam irradiated to a detector 111 expanded by a thermal lens generated at the light focusing portion of the excitation light L1 in the sample 109. A change amount of the spreading angle of the probe light L2 is proportional to concentration of the sample 109, and an incident light amount with respect to the detector 111 is changed. Therefore, the sample concentration can be measured from a detection signal of the detector 111.
FIG. 6B is a schematic configuration diagram illustrating an exemplary related art in which a photothermal conversion spectroscopic analyzer 303 uses a reflection optical system (JP-04-369467-A).
Proposed is the photothermal conversion spectroscopic analyzer 303 using the reflection optical system in which a laser beam having passed through a sample is reflected at a reflector and made to enter a light focusing optical system, and then analysis is performed by utilizing the reflected light. According to JP-04-369467-A, a single beam method in which a probe light L2 is also used as an excitation light is adopted, and the probe light L2 is focused by a first condenser lens 106 to a reflector 113 disposed outside the sample 109 and the sample cell 107. The probe light L2 reflected at the reflector 113 is guided by a filter 121 toward a detector 124 formed of a second condenser lens 118, a cylindrical lens 122, and a light receiving element 123, and then a thermal lens signal is measured.